This invention relates to medical electrical stimulation electrodes in general and to subcutaneous defibrillation electrodes in particular.
In the past years, there has been a substantial activity directed toward development of a practical implantable defibrillator. Some approaches, such as those disclosed in U.S. Pat. No. 3,942,536 issued to Mirowski et al and U.S. Pat. No. 4,161,952 issued to Kinney et al have employed only endocardial electrodes. Alternate approaches to this problem have focused on systems employing one or more epicardial electrodes as alternatives to or in addition to endocardial electrodes. Some such systems are disclosed in U.S. Pat. No. 4,030,509 issued to Heilman et al and U.S. Pat. No. 4,291,707 issued to Heilman et al.
Use of epicardial electrodes has the disadvantage that it requires major surgery in order to mount the electrodes to the epicardium. Therefore, more recent approaches to the problem of an implantable defibrillator have employed a combination of endocardial and subcutaneous electrodes, rather than epicardial electrodes. One such system is disclosed in U.S. Pat. No. 4,727,877 issued to Kallok. Researchers have sometimes accomplished this change by simply implanting available epicardial electrodes subcutaneously.